No abstract

Effects of the molecular weight on the crystallization behaviour of branched polyethylene become observable if isothermal crystallization is studied at temperatures near to the melting end. Crystallinifies decrease with decreasing molecular weight. Thicknesses of lamellae grown during isothermal crystallization are independent of the molecular weight. They depend only on temperature. Compared to the effect of the branches polydispersity gives only a minor contribution to the broadening of the crystallization and melting range of low density polyethylene.

Solutions of poly(decy1 methacrylate) in isooctane (2,2,4-trimethylpentane) show lower critical solution temperatures (LCST) that lie well below the thermal degradation of the polymer. The corresponding exothermal theta-temperature (from the Shultz-Flory plot) amounts to 210°C. The increase in solvent quality by pressure turns out to be very pronounced (d T,/dp = + 1 K/bar). With solutions of the polymer in motor oils, high temperature demixing is unlikely to occur below their boiling point. The theoretical evaluation of published experimental data for 1 1 different systems exhibiting LCSTs demonstrates the following: Under the equilibrium vapour pressure of the solution high temperature demixing is generally observed within the temperature interval between T,, the boiling point of the pure solvent (1 bar), and 1,s Tb. As T, -Tb increases, the heats of mixing and the pressure influence on T, increase, too.

Poly(n-decyl methacrylate), a statistical copolymer of ethylene and propylene, and a diblock copolymer of styrene and hydrogenated butadiene were studied as representatives of various kinds of viscosity-index (VI) improvers. Essomarcol52 and AF 1 from Schindler served as base-oils, toluene and 1-phenyl dodecane were also studied. By means of viscosity measurements in the temperature interval from 37.8 to 98.9OC up to a concentration of typically 1 wt.-070 polymer, the viscosity indices of the different systems and the corresponding intrinsic viscosities, Huggins coefficients, and activation energies of flow, E* , were determined. The discussion of the obtained experimental material demonstrates that the VI of a base-oil can be raised in two clearly distinguishable ways: (i) via an increase in the viscosity due to the mere presence of the polymer, without a change in E* and (ii), less general, via an additional reduction of E + as a consequence of thermodynamic interactions.Formulae are given from which these two contributions can be calculated. ZUS AMMENFASSUNG:Poly (n-decylmethacrylat), ein statistisches Copolymeres aus Ethylen und Propylen, und ein Zweiblockcopolymeres aus Styrol und hydriertem Butadien wurden reprbentativ fUr verschiedene Arten von Viskosittitsindex-Verbesserern untersucht. Essomar-col52 und AF 1 von Schindler dienten als Ole; Toluol und 1 Phenyldodecan wurden ebenfalls untersucht. Mit Hilfe von Viskosittitsmessungen im Temperaturbereich von 37,8 bis 98,9OC und bis zu einer Polymerkonzentration von 1 Gew.-% wurden die Viskosittitsindizes und die entsprechenden Grenzviskosittitszahlen, Huggins-Koeffizienten sowie FlieR-Aktivierungsenergien, E* , verschiedener Systeme bestimmt. Die ErOrterung der experimentellen Ergebnisse zeigt , dal3 der Viskosittitsindex von 6 1 auf zwei unterschiedliche Arten erh6ht werden kann: (i) durch ErhOhung der Viskosittit a Present address: ENKA AG, Research Institute Obernburg, D-8753 Obernburg, FRG. 0 1988 HUthig & Wepf Verlag, Basel 0003-3146/88/%03.00 157 E. Maderek and B. A. Wolf aufgrund der blol3en Anwesenheit von Polymeren ohne Vertinderung von E+ und (ii), weniger hlufig, durch Verringerung von E + als Folge der thermodynamischen Wechselwirkung. Es werden Gleichungen angegeben, die es erlauben, diese beiden Beitrlge zu berechnen .

A branched polyethylene with broad molecular weight distribution was separated into a series of fractions by fractional precipitation from dilute solution. The fractions were characterized by viscometric and density measurements, IR-spectroscopy and calorimetry. The methyl group content and the density turned out as lhgely constant. Molecular weight effects show up in the melting behaviour. The main range of melting and the end of the melting curve shift to lower temperatures with decreasing molecular weight. Compared to the overall extension of the melting range these shifts are small. One has to conclude that polydispersity gives only a minor contribution to the broadening of the melting range, partial melting being mainly caused by the branches.0025-1 16X/83/$03.00